Selenium crystallization induced by corotron charging

Amorphous selenium films were exposed to corotron charging and simultaneous photo discharging. Corotron charging increased considerably the rate of crystallization compared to photocrystallization. This increase was manifested as a higher top surface nucleation rate in the corotron charged regions. An ion recombination mechanism is proposed to explain the enhanced crystallization due to corotron charging.     

Ice crystallization induced by optical breakdown

Ice crystallization in supercooled water has been initiated by focused Nd:YAG laser pulses at 1064 nm wavelength. The pulses of 8 ns duration and up to 2 mJ energy produce a bubble in the supercooled liquid after optical breakdown and plasma formation. The subsequent collapse and disintegration of the bubble into fragments was observed to be followed by ice crystal nucleation in many, but not all cases. Details of the crystallization events have been investigated by high-speed imaging, and nucleation statistics and crystal growth rates are given. It is argued that homogeneous nucleation in the compressed liquid phase is a plausible explanation of the effect.     

Atomic scale conductance induced by single impurity charging

A scanning tunneling microscope was used to probe electron transport through an alkali doped C(60) monolayer crystal on Al(2)O(3) grown by the oxidation of NiAl(110). Each individual alkali atom forms a localized complex with the neighboring C(60) molecules. Charging of the complex induces a substantial rise in the current that persists outside the physical dimensions of the complex. This induction of the current rise is characterized by spatially resolved spectroscopy and mapping of the differential conductance (dI/dV) in the vicinity of the complex.     

Polycrystalline silicon thin films prepared by Ni silicide induced crystallization and the dopant effects on the crystallization

Intrinsic and doped polycrystalline silicon thin films were grown by the Ni silicide seeds induced crystallization. The Ni first reacted to Si forming a silicide seeds, then these seeds act as nuclei, from which the grains start to grow laterally. Compared with traditional Ni induced lateral crystallization, polycrystalline silicon thin film was grown by Ni silicide induced crystallization with low Ni contamination and large grain sizes. It can be found that the Ni silicide induced crystallization rate is accelerated by p-type doping and is decelerated by n-type doping. And the slightly and strongly phosphorous-doped polycrystalline silicon can be obtained with different grain shapes. Also, the sheet resistance of doped polycrystalline silicon decreases with the increasing of the doping atoms. A reasonable explanation is presented for the dopant effects on the growth rate, microstructure and electronic properties of the samples.     

Solution-based metal induced crystallization of a-Si

This paper investigates a simplified metal induced crystallization (MIC) of a-Si, named solution-based MIC (S-MIC). The nickel inducing source was formed on a-Si from salt solution dissolved in de-ionized water or ethanol. a-Si thin film was deposited with low pressure chemical vapour deposition or plasma enhanced chemical vapour deposition as precursor material for MIC. It finds that the content of nickel source formed on a-Si can be controlled by solution concentration and dipping time. The dependence of crystallization rate of a-Si on annealing time illustrated that the linear density of nickel source was another critical factor that affects the crystallization of a-Si, besides the diffusion of nickel disilicide. The highest electron Hall mobility of thus prepared S-MIC poly-Si is 45.6cm²/(V.s). By using this S-MIC poly-Si, thin film transistors and display scan drivers were made, and their characteristics are presented.     

Development of polycrystalline silicon films on flexible metallic substrates by aluminium induced crystallization

Thin film silicon solar cells on low cost foreign substrates could be attractive for highly efficient and low cost production of photovoltaic electricity. An attempt has been made to synthesise high-quality continuous polycrystalline silicon (pc-Si) layers on flexible metallic substrates using aluminium induced crystallization (AIC) for the first time. Amorphous silicon films deposited by ECR-PECVD were crystallized on diffusion barrier coated metallic substrates at lower temperatures (<577°C). The crystallization was studied using Raman as well as UV reflectance spectroscopy. The as-grown AIC pc-Si films were found to be continuous and densely packed without amorphous phase. The migration of impurities from the substrate to the pc-Si films and the conformability of the barrier layer with the substrate and pc-Si films were studied systematically in terms of chemical and stress level analysis, which are the important aspects to be considered when metallic foils are used as substrates. It was observed that the barrier layer also serves as a buffer layer to minimise the stress level enormously in the AIC grown pc-Si layer, though the supporting material has a thermal expansion coefficient of higher order at higher annealing temperatures. The present investigation proves the possibility to grow better-quality polycrystalline silicon films on flexible metallic foils and further demonstrates the steps that need to be considered to improve the quality of AIC pc-Si films as well as the strength of the barrier layer.     

Skeletonization by crystallization

A skeleton of a planar contour is a set of centres of bitangent circles lying inside the contour. If contour of a planar shape was made up of a spatial distribution of sodium acetate crystals the propagating crystallization patterns would implement distance transformation, or thinning, of the contour. In such a case, boundaries between colliding patterns represent skeleton of the planar shape. In laboratory experiments we demonstrate that a supersaturated solution of a sodium acetate is a massively parallel processor. In this sodium-acetate processor data are inputted as spatial distribution of nucleation sites, information is transmitted via propagating patterns of crystallization and results of computation are represented by boundaries between stationary domains of crystals.     

Effects of corotron size and parameters on the dielectric substrate surface charge

Effects of variation of parameters of a corona device (corotron) used in electro-photographic machines on the amount of surface charge build-up on the surface of dielectric substrate were studied. Particular attention was given to the effect of corotron dimension including wire–shields and wire–plate distances, substrate thickness, shields insulation and the substrate speed on the amount of substrate surface charge. The computational analyses were performed for a two-dimensional cross-section of the corotron under steady-state condition. The Maxwell equations were solved and the electrical quantities in a rectangular positive single wire corotron were evaluated. The simulation results showed that for a fixed wire voltage, the corotron size, the substrate thickness, insulation of shields and the substrate speed will affect the distributions of electrical quantities in the corotron. The wire–substrate distance and the substrate speed, however, were found to be the main parameters that control the amount of surface charge build-up on the substrate.     

TEM studies on the formation of nano crystallites of Si by metal induced crystallization

In the present investigations, we have grown the nano-crystallites of Si by metal induced crystallization process. Layers of two different metals (Al and Au) were deposited on either side of Si using thermal evaporation technique to study metal induced crystallization. Annealing of such samples was carried out in the hot stage of TEM. We have found that the crystallization of amorphous silicon starts at 150 °C through the formation of metal silicides. Formation of metal silicides was observed through selected area diffraction. Nearly complete formation of nano crystallites of Si throughout the sample was observed at 200 °C. High-resolution TEM studies confirm the formation of nano-crystallites of Si all along the film.     

Nickel induced lateral crystallization behavior of amorphous silicon films

Nickel induced lateral crystallization of amorphous silicon with and without electric field has been studied. Dendritic silicon growth behavior is observed, with crystallites of a few hundred nanometers in width and up to a few microns in length. The behavior can be understood from the preferential epitaxial growth of silicon from the (1 1 1) facets of the NiSi₂ precipitate, which forms during the early stage of the annealing process. The dendritic growth fronts are different with and without electric field in the nickel induced lateral crystallization process. Electric field is found to be beneficial in increasing the lateral crystallization rate and improving the film crystallinity. Joule heating plays an important role as well to enhance the lateral crystallization.     

Strain rate induced crystallization in bulk metallic glass-forming liquid

We report on the solidification of Au49, Ag5.5, Pd2.3, Cu26.9, Si16.3 bulk metallic glass under various strain rates. Using a copper mold casting technique with a low strain rate during solidification, this alloy is capable of forming glassy rods of at least 5 mm in diameter. Surprisingly, when the liquid alloy is splat cooled at much higher cooling rates and large strain rates, the solidified alloy is no longer fully amorphous. Our finding suggests that the large strain rate during splat cooling induces crystallization. The pronounced difference in crystallization behavior cannot be explained by the previously observed strain rate effect on viscosity alone. A strain rate induced phase separation process is suggested as one of the explanations for this crystallization behavior. The strain-rate-dependent critical cooling rate must be considered in order to assess the intrinsic glass forming ability of metallic liquid.     

Chiral symmetry breaking during crystallization: complete chiral purity induced by nonlinear autocatalysis and recycling

We report experimental results that show a large and symmetric population of D and L crystals moving into complete chiral purity, with one of the enantiomers completely disappearing. The results indicate (i) a new symmetry breaking process incompatible with the hypothesis of an initial single chiral phase or "mother crystal," (ii) that total symmetry breaking and complete chiral purity can be achieved from a system that initially includes both enantiomers, and (iii) that this is achieved through a nonlinear autocatalytic-recycling process.     

用电容充电法测量普朗克常量

提出一种利用光电管产生的光电流给电容充电来准确测量光电管截止电压的方法,从而得到普朗克常量.实验中采用了6种颜色的LED器件做光源直接照射光电管上,并通过具有高输入阻抗的数据采集卡实时测量电容两端的电压.实验测得的普朗克常量值与公认值的误差小于3％.     

Laser- and gamma-ray induced crystallization of IR-transmitting calcium gallate glass

Ar⁺-laser (=488 nm) irradiation of calcium gallate (CG) glass with the composition of 60CaO·39Ga₂O₃·Fe₂O₃ resulted in a distinct decrease in the IR transmittance (T) due to the formation of crystalline CaGa₂O₄ and CaGa₄O₉ phases. The Mössbauer spectrum of non-irradiated glass comprised a broad doublet due to distorted Fe³⁺(T_d) with, , and of 0.20, 1.33, and 1.00 mm s^–1, respectively. An additional doublet due to Fe³⁺(T_d) was observed in the Ar⁺-irradiated glass and, , and were 0.17, 1.32, and 0.75 mm s^–1, respectively. A decrease inT was also observed after the⁶⁰Co -ray irradiation with doses 10⁵Gy, and the precipitation of CaO, Ga₂O₃, and CaGa₄O₇ phases was confirmed by X-ray diffraction.     

Hydrodynamically induced crystallization of polymers from solution. VI. Amylose

A study has been made of the crystallization of amylose from stirred solutions. It was found that a highly turbulent flow can induce fibrillar crystallization in a 5% solution of amylose in 1 N KOH and in 35% chloral hydrate. Furthermore it was observed that these fibrillar crystals were insoluble in the original solution after crystallization.

Electron microscopic investigations revealed the presence of long fibrils, sometimes aggregated to larger units. Some fibers displayed transverse striations resembling the well-known shish-kebab structures. Treatment of the fibrillar crystals with iodine yielded the well-known blue coloring characteristic for amylose. However, in the electron microscope it was seen that only discrete portions of the fibers were stained.

Stirring of aqueous n-butanol solutions of amylose resulted in the formation of small rodlike fibrils in addition to lath-shaped single crystals to which a large number of tentacles were attached.

Rectangular-shaped crystals, grown in quiescent solutions, were deformed in a narrow gap couette instrument into long irregular fibers.     

原子荧光光谱法测定海藻泥中的总硒以及无机硒

采用湿法消解处理样品,利用双通道原子荧光光谱法测定海藻泥中的总硒及无机硒的含量.讨论了各种对测定有影响的因素,并优化了分析条件.在最佳实验条件下,Se的检出限为0.2410ng/mL,此方法快速、简便、准确且灵敏度高,为海藻中硒含量测定提供了较好的方法.     

氢化物原子荧光法(HG-AFS)测定鸡蛋中的硒

本文建立了一种HG－AFS法测定食疗蛋中硒的方法，该方法简单，快速，同时也提高了分析的灵敏度。方法的检出限为0.3μg/L，食疗蛋中硒的样品测定的相对标准偏差＜10％，回收率在90％以上。     

Predicting the electrostatic charging behavior of insulating materials without charging tests

It is well known that experiments of charging and later discharging of materials with gas ignition probes or hand-coulombmeters show that some insulating materials do exist that cannot be hazardously charged by manual rubbing in spite of their high surface resistance. In this work, effects of variations of physical and chemical properties as well as the structure of these materials have been systematically investigated. The results obtained help to explain this behavior and propose approaches to predict the charging behavior of such insulating materials without any charging test at all.     

硒形态流动注射催化光度法分析

基于在pH7的柠檬酸磷酸氢二钠缓冲溶液中,硒(Ⅳ)对Na2S还原天青Ⅰ有强催化作用,建立了流动注射催化光度法测定硒的新方法。考察了不同流路的影响,分别研究了试剂和试样的流速、反应介质及酸度、反应温度、共存物质的影响。利用单纯形优化法选择了各种试剂的最佳用量以及采样体积、反应管长的最佳实验条件。方法的线性范围为01～20mg·L-1,检出限为0015mg·L-1,相对标准偏差小于31%,进样频率为120个·h-1。该方法用于大蒜和硒酵母中有机硒和无机硒的测定,结果发现大蒜对硒有强的富集作用,有机硒的转化率随环境硒浓度的增加而下降。测定的回收率在971%～1043%。     

Control of size and shape of ncSi in aSiNx/aSi:H multilayers by laser induced constrained crystallization

Size-controlled nanocrystalline silicon (ncSi) has been prepared from aSiN_x/aSi:H multilayers by pulsed laser induced crystallization. Transmission electron microscopy (TEM) analyses show that the growth of ncSi is constrained by the aSiN_x/aSi:H interface, and the size of ncSi is controlled by the laser energy density and the aSi sublayer thickness when the aSi sublayer thickness is less than 10 nm. On the basis of the experimental results, we discuss the transitional process from the spherical shape to the cylindrical shape in the growth model of ncSi crystallization. The constrained effect for the crystal growth increases with a decrease of the aSi sublayer thickness. The critical thickness of the aSi sublayer for constrained crystallization can be determined by the present model. Moreover, the increase of the crystallization temperature in the ultra-thin aSi sublayer can be explained. PACS 68.65.+g; 81.40.Ef; 68.35.-p; 61.16.Bg; 61.46.+w